Antioxidants Could Be Terrible For People Who Already Have Cancer

We've heard over and over that foods high in compounds called antioxidants are good for you — they're even often called "superfoods." But in reality, we don't know much about how antioxidants work in the body and what health effects they might have.

Antioxidants neutralize "free radicals" — molecules that can harm cells. In theory, that's a good thing.

The researchers found that adding Vitamin E to the diets of mice with early-stage lung cancer "markedly increases tumor progression and reduces survival."

The results were clear. And alarming.

"Their tumors accelerated in growth, became more invasive, and killed the mice twice as fast compared to mice with early lung tumors that didn’t receive antioxidants," the press release explains. That effect held true with a very different antioxidant called NAC, suggesting that it's probably not just Vitamin E that's a problem — it's antioxidants in general.

It's important to underscore that while we often study disease in rodents, mice are not exactly like humans. Cancer findings cannot just be generalized from mice to people. The researchers saw similar results with human cancer cells in a petri dish, but those also behave very differently than cancer cells inside the body.

But this isn't the first study to suggest that antioxidants may increase — not decrease — cancer risk.

Taken as a whole, recent research suggests the same conclusion: Antioxidants are probably bad for people who have cancer or are at high risk for cancer.

What's going on?

Using a mouse model, the authors show that the antioxidants inactivated the protein p53, which typically protects cells from the dangers of broken DNA. Broken strands of DNA cause mutations that can make the cell grow out of control and start to move through the body — the hallmarks of cancer.

According to study author Per Lindahl of the University of Gothenberg, "the body has evolved a defense system which is based on the p53 protein, and that protein can sense when DNA becomes damaged. And when it senses damaged DNA, it can force the cell to cease to proliferate, to stop dividing, or even to commit suicide... Thereby, it can prevent tumors from growing or cancer from developing."

But in the presence of antioxidants, the cell's DNA is better protected against damage. As a result, the cell's natural protective process is no longer on high alert. It gets lazy, like a napping security guard, and cells with cancerous mutations start to multiply.

What's next?

First off, it's not exactly clear how the amount of NAC and Vitamin E given to the mice equates to the amount that might be ingested by humans, though this is an important question. Figuring out how these studies might transfer to humans, and the levels needed for antioxidants to become potentially dangerous, are two important next steps.

The study may be especially relevant to people with "chronic obstructive pulmonary disease, who are often smokers with an increased risk of developing lung cancer." Frighteningly, this group often takes large quantities of NAC to relieve mucous buildup.

One key limitation of the study, the authors write, is that it only looked at "the impact of antioxidants on tumor progression, and not tumor initiation or prevention."

The researchers also looked at lung cancer only and left open the question of whether antioxidants may well do good in people who aren't at high risk for cancer, or in protecting against other kinds of cancer.

Still, the tide is clearly turning against previous advice that indicated antioxidants were some of our most reliable anti-cancer agents.

"The time has come to seriously ask whether antioxidant use much more likely causes than prevents cancer," Nobel Laureate James Watson cautioned in an editorial published last year in Open Biology.

He went on:

All in all, the by now vast number of nutritional intervention trials using the antioxidants β-carotene, vitamin A, vitamin C, vitamin E and selenium have shown no obvious effectiveness in preventing gastrointestinal cancer nor in lengthening mortality. In fact, they seem to slightly shorten the lives of those who take them. Future data may, in fact, show that antioxidant use, particularly that of vitamin E, leads to a small number of cancers that would not have come into existence but for antioxidant supplementation. Blueberries best be eaten because they taste good, not because their consumption will lead to less cancer.